The present invention relates to a novel process for the preparation of 3,3'- or 3,4'-diaminodiphenylmethane.
3,3'-Diaminodiphenylmethane and 3,4'-diaminodiphenylmethane are useful as monomers for the production of high-molecular compounds, intermediates for the production of agricultural chemicals, pharmacological compounds and dyes, particularly useful as starting materials for the production of polyamides and polyimides having excellent heat resistance.
Herefore, 3,3'-diaminodiphenylmethane has been prepared by condensing 3-nitrobenzyl alcohol with nitrobenzene or condensing nitrobenzene with formaldehyde to prepare 3,3'-dinitrodiphenylmethane which is then reduced in the presence of stannic chloride or iron [L. Gatterman et al., Ber., 27, 2295 (1894); L. Thorp et al., J. Am. Chem. Soc., 37, 373 (1915); M. Schopff et al., Ber., 27, 2322 (1894)].
3,4'-Diaminodiphenylmethane has been prepared by condensing 4-nitrobenzyl alcohol with nitrobenzene to prepare 3,4'-dinitrodiphenylmethane which is then reduced [L. Gattarmann et al., Ber., 27, 2293 (1894)].
However, even when the condensation reaction between benzyl alcohol and nitrobenzene or between nitrobenzene and formalin is conducted for a long period of time by using a large amount of concentrated sulfuric acid, these processes result in yields of dinitrodiphenylmethane of as low as only 20 to 30%. Further, dinitrodiphenylmethane must be reduced in the presence of a tin compound or iron to obtain diaminodiphenylmethane. But, it is bothersome to separate the metallic compound used for the reduction from the product and it is necessary to pay attention lest trace amounts of the metal should remain in the product.
Thus the conventional processes of preparing dinitrodiphenylmethane by the known condensation reaction and reducing it to prepare diaminodiphenylmethane have disadvantages in that they require much cost and effort for the disposal of a large amount of various waste materials to prevent them from causing environmental pollution or for the recovery of them, and in addition thereto the desired product is obtained in a low yield. Accordingly, these processes are industrially unfavorable from the viewpoints of economy and environmental protection.